Up to the present day, together with the development of wireless communication technology, Long Term Evolution (LTE) has become widespread as a new wireless communication standard as an alternative to Wideband Code Division Multiple Access (WCDMA). A mobile station such as a mobile telephone connects to a base station that supports a wireless communication scheme such as WCDMA and LTE, and communicates with another mobile station. These kinds of wireless communication schemes are referred to as radio access technology (RAT), and among mobile stations there is also a mobile station (hereafter denoted as a “dual terminal”) with which communication by means of a plurality of different RATs is possible. A home subscriber server (HSS), which is a higher-level device of the base station, determines a RAT to be used by the dual terminal for standby, in accordance with the contractual information and capacity of the dual terminal (whether or not LTE is supported, for example). When the dual terminal receives notification of the determined RAT from the connection-destination base station, the dual terminal performs a standby process using the RAT designated by the base station, out of a plurality of available RATs. Japanese Laid-open Patent Publication No. 2003-125450 and 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 25.331 V11.2.0 (2012-June) 8.1.3.3 are examples of related art.